Abstract
Infectious bronchitis (IB), caused by the Infectious bronchitis virus (IBV), remains a formidable challenge to the poultry industry worldwide, owing to its multi-systemic nature and the continual emergence of diverse viral variants that undermine vaccine efficacy. Despite widespread vaccination efforts, controlling IBV in regions like Kerala is particularly challenging due to inconsistent vaccination practices and the documented presence of the disease. This study set out to characterize IBV isolates circulating in Kerala, with a focus on assessing their genetic diversity and pathological impact. Field samples (n = 80) were screened using reverse transcriptase polymerase chain reaction (RT-PCR) targeting the hypervariable region 3 of the S1 subunit, leading to the detection of IBV in 32 samples. Virus isolation was successfully achieved from these positive samples using embryonated eggs, with subsequent confirmation via RT-PCR using the same set of primers. From the confirmed positive samples, we amplified the full S1 subunit of the S gene as well as the M and N genes, and the resulting products were sequenced. Comparative analyses were conducted against the widely used vaccine strain H120 and other Indian IBV isolates deposited in GenBank. Phylogenetic analysis indicated that the Kerala isolates clustered together with other isolates from different parts of India. Histopathological examination of key organs revealed characteristic lesions, offering insights into the virus's tissue tropism. The findings underscore the significant genetic variability among IBV strains in Kerala and highlight the critical need for region-specific vaccination strategies to achieve effective disease management.